Collimating lens

ABSTRACT

A collimating lens includes at least two lens groups, each having an aspherical surface. The collimating lens also includes a flat diffraction lens disposed nearest to an image plane.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a collimating lens, and moreparticularly to a collimating lens with a diffraction lens.

2. Description of Related Art

A collimating lens is an optical device that aligns light beams in aspecific direction to make collimated light or parallel rays.Accordingly, light does not disperse with distance, or at least, willdisperse minimally. The collimating lens may be used with a light sourcesuch as a laser diode.

A conventional collimating lens may consist of a mould-made curved lenscomposed of glass. As a result, cost is high and overall dimension islarge. Moreover, the conventional collimating lens possesses at leastone convex surface, which makes assembling the collimating lensdifficult.

For the foregoing reasons, a need has arisen to propose a novelcollimating lens to eliminate drawbacks of the conventional collimatinglens.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the embodiment of thepresent invention to provide a collimating lens with compact dimensionat low cost to facilitate the assembly of the collimating lens.

According to one embodiment, a collimating lens includes at least twolens groups, each having an aspherical surface. The collimating lensincludes a flat diffraction lens disposed nearest to an image plane. Thecollimating lens of one embodiment possesses no convex outer surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a lens arrangement of a collimating lens according to afirst embodiment of the present invention;

FIG. 1B shows an exemplary ray diagram of FIG. 1A;

FIG. 2A shows a lens arrangement of a collimating lens according to asecond embodiment of the present invention;

FIG. 2B shows an exemplary ray diagram of FIG. 2A;

FIG. 3A shows a lens arrangement of a collimating lens according to athird embodiment of the present invention; and

FIG. 3B shows an exemplary ray diagram of FIG. 3A.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A shows a lens arrangement of a collimating lens 100 according toa first embodiment of the present invention, and FIG. 1B shows anexemplary ray diagram of FIG. 1A. The collimating lens 100 of the firstembodiment and collimating lenses of other embodiments as described inthe specification may be preferably fabricated by wafer-level optics(WLO) technique. The collimating lens 100 of the first embodiment andcollimating lenses of other embodiments as described in thespecification may be composed of a transparent material such as glass orplastic. In the drawing, the left-hand side of the collimating lens 100faces an object, and the right-hand side of the collimating lens 100faces an image plane.

In the first embodiment, the collimating lens 100 may include a firstlens group 1, a second lens group 2 and a third lens group 3 in theorder from the object side to the image side. Specifically, the firstlens group 1 may include, in the order from the object side to the imageside, a negative-powered first lens 11 (that is, a lens with negativerefractive power), a flat second lens 12 (that is, a lens with a planarobject-side surface and a planar image-side surface), and apositive-powered third lens 13 (that is, a lens with positive refractivepower). To be more specific, the negative-powered first lens 11 has anaspherical concave object-side surface s1 (with a negative radius) and aplanar image-side surface s2. The flat second lens 12 has a planarobject-side surface s2 and a planar image-side surface s3. Thepositive-powered third lens 13 has a planar object-side surface s3 andan aspherical convex image-side surface s4. In the embodiment, thenegative-powered first lens 11 is in substantially contact with the flatsecond lens 12, which is further in substantially contact with thepositive-powered third lens 13.

The second lens group 2 may include, in the order from the object sideto the image side, a negative-powered fourth lens 14, a flat fifth lens15, and a positive-powered sixth lens 16. To be more specific, thenegative-powered fourth lens 14 has an aspherical concave object-sidesurface s5 (with a negative radius) and a planar image-side surface s6.The flat fifth lens 15 has a planar object-side surface s6 and a planarimage-side surface s7. The positive-powered sixth lens 16 has a planarobject-side surface s7 and an aspherical convex image-side surface s8.In the embodiment, the negative-powered fourth lens 14 is insubstantially contact with the flat fifth lens 15, which is further insubstantially contact with the positive-powered sixth lens 16.

The third lens group 3 may include, in the order from the object side tothe image side, a positive-powered seventh lens 17, a flat eighth lens18, and a flat diffraction ninth lens 19. To be more specific, thepositive-powered seventh lens 17 has an aspherical convex object-sidesurface s9 (with a positive radius) and a planar image-side surface s10.The flat eighth lens 18 has a planar object-side surface s10 and aplanar image-side surface s11. The flat diffraction ninth lens 19 has aplanar object-side surface s11 and a planar image-side surface s12. Inthe embodiment, the positive-powered seventh lens 17 is in substantiallycontact with the flat eighth lens 18, which is further in substantiallycontact with the flat diffraction ninth lens 19.

Generally speaking, the collimating lens 100 of the embodiment has atleast two aspherical surfaces, one of which has a positive radius andthe other of which has a negative radius. For example, the collimatinglens 100 has the aspherical concave object-side surface s1 with anegative radius and the aspherical convex object-side surface s9 with apositive radius.

According to one aspect of the embodiment, the negative-powered firstlens 11, the positive-powered third lens 13, the negative-powered fourthlens 14, the positive-powered sixth lens 16, the positive-poweredseventh lens 17 and the flat diffraction ninth lens 19 have a refractiveindex ranging between 1.5 and 1.6, and have an Abbe number rangingbetween 31 and 48.

According to another aspect of the embodiment, the flat second lens 12,the flat fifth lens 15 and the flat eighth lens 18 have a refractiveindex ranging between 1.5 and 1.6, and have an Abbe number rangingbetween 45 and 65.

FIG. 2A shows a lens arrangement of a collimating lens 200 according toa second embodiment of the present invention, and FIG. 2B shows anexemplary ray diagram of FIG. 2A.

In the second embodiment, the collimating lens 200 may include a firstlens group 4 and a second lens group 5 in the order from the object sideto the image side. Specifically, the first lens group 4 may include, inthe order from the object side to the image side, a flat first lens 21and a negative-powered second lens 22. To be more specific, the flatfirst lens 21 has a planar object-side surface t1 and a planarimage-side surface t2. The negative-powered second lens 22 has a planarobject-side surface t2 and an aspherical concave image-side surface t3(with a negative radius). In the embodiment, the flat first lens 21 isin substantially contact with the negative-powered second lens 22.

The second lens group 5 may include, in the order from the object sideto the image side, a positive-powered third lens 23, a flat fourth lens24, and a flat diffraction fifth lens 25. To be more specific, thepositive-powered third lens 23 has an aspherical convex object-sidesurface t4 (with a positive radius) and a planar image-side surface t5.The flat fourth lens 24 has a planar object-side surface t5 and a planarimage-side surface t6. The flat diffraction fifth lens 25 has a planarobject-side surface t6 and a planar image-side surface t7. In theembodiment, the positive-powered third lens 23 is in substantiallycontact with the flat fourth lens 24, which is further in substantiallycontact with the flat diffraction fifth lens 25.

The collimating lens 200 of the second embodiment may further include aring spacer 26, which is disposed between and in contact withperipheries of the first lens group 4 and the second lens group 5, suchthat the first lens group 4 may be coupled with the second lend group 5.

Generally speaking, the collimating lens 200 of the embodiment has atleast two aspherical surfaces, one of which has a positive radius andthe other of which has a negative radius. For example, the collimatinglens 200 has the aspherical concave image-side surface t3 with anegative radius and the aspherical convex object-side surface t4 with apositive radius.

According to one aspect of the embodiment, the negative-powered secondlens 22, the positive-powered third lens 23 and the flat diffractionfifth lens 25 have a refractive index ranging between 1.5 and 1.6, andhave an Abbe number ranging between 31 and 48.

According to another aspect of the embodiment, the flat first lens 21and the flat fourth lens 24 have a refractive index ranging between 1.5and 1.6, and have an Abbe number ranging between 45 and 65.

FIG. 3A shows a lens arrangement of a collimating lens 300 according toa third embodiment of the present invention, and FIG. 3B shows anexemplary ray diagram of FIG. 3A.

In the third embodiment, the collimating lens 300 may include a firstlens group 6 and a second lens group 7 in the order from the object sideto the image side. Specifically, the first lens group 6 may include, inthe order from the object side to the image side, a flat first lens 31and a positive-powered second lens 32. To be more specific, the flatfirst lens 31 has a planar object-side surface m1 and a planarimage-side surface m2. The positive-powered second lens 32 has a planarobject-side surface m2 and an aspherical convex image-side surface m3(with a positive radius). In the embodiment, the flat first lens 31 isin substantially contact with the positive-powered second lens 32.

The second lens group 7 may include, in the order from the object sideto the image side, a positive-powered third lens 33, a flat fourth lens34, and a flat diffraction fifth lens 35. To be more specific, thepositive-powered third lens 33 has an aspherical convex object-sidesurface m4 (with a positive radius) and a planar image-side surface m5.The flat fourth lens 34 has a planar object-side surface m5 and a planarimage-side surface m6. The flat diffraction fifth lens 35 has a planarobject-side surface m6 and a planar image-side surface m7. In theembodiment, the positive-powered third lens 33 is in substantiallycontact with the flat fourth lens 34, which is in substantially contactwith the flat diffraction fifth lens 35.

The collimating lens 300 of the third embodiment may further include aring spacer 36, which is disposed between and in contact withperipheries of the first lens group 6 and the second lens group 7, suchthat the first lens group 6 may be coupled with the second lend group 7.

Generally speaking, the collimating lens 300 of the embodiment has atleast two aspherical surfaces. For example, the collimating lens 300 hasthe aspherical convex image-side surface m3 and the aspherical convexobject-side surface m4.

According to one aspect of the embodiment, the positive-powered secondlens 32, the positive-powered third lens 33 and the flat diffractionfifth lens 35 have a refractive index ranging between 1.5 and 1.6, andhave an Abbe number ranging between 31 and 48.

According to another aspect of the embodiment, the flat first lens 31and the flat fourth lens 34 have a refractive index ranging between 1.5and 1.6, and have an Abbe number ranging between 45 and 65.

According to the embodiments discussed above, a collimating lens withreduced dimension may be made by wafer-level optics (WLO) technique atlow cost. Moreover, the collimating lens of the embodiments possesses noconvex outer surface, thereby facilitating the assembly of thecollimating lens.

Moreover, as the flat diffraction lens (19, 25 or 35) has a planarimage-side surface (s12, t7 or m7), on which a diffractive opticalelements (DOEs) pattern (not shown) may be directly formed, anadditional glass plate as in the conventional art is thus not requiredand may be omitted, thereby reducing the thickness of the collimatinglens.

The aspheric surface (e.g., s1, s4, s5, s8, s9, t3, t4, m3 or m4) may bedefined by the following equation:

$z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {( {1 + k} )c^{2}r^{2}}}} + {\alpha_{1}r^{2}} + {\alpha_{2}r^{4}} + {\alpha_{3}r^{6}} + {\alpha_{4}r^{8}} + {\alpha_{5}r^{10}} + {\alpha_{6}r^{12}} + {\alpha_{7}r^{14}} + {\alpha_{8}r^{16}}}$where z is a distance from a vertex of lens in an optical axisdirection, r is a distance in the direction perpendicular to the opticalaxis, c is a reciprocal of radius of curvature on vertex of lens, k is aconic constant and α₁ to α₈ are aspheric coefficients.

Although specific embodiments have been illustrated and described, itwill be appreciated by those skilled in the art that variousmodifications may be made without departing from the scope of thepresent invention, which is intended to be limited solely by theappended claims.

What is claimed is:
 1. A collimating lens, comprising: at least two lensgroups, each having an aspherical surface; and a flat diffraction lensarranged in one of the at least two lens groups, and the flatdiffraction lens disposed nearest to an image plane; wherein oneaspherical surface of the at least two lens groups has a positiveradius, and another aspherical surface of the at least two lens groupshas a negative radius.
 2. The collimating lens of claim 1, wherein theat least two lens groups are composed of a plurality of lens having arefractive index ranging between 1.5 and 1.6, and the flat diffractionlens has a refractive index ranging between 1.5 and 1.6.
 3. Thecollimating lens of claim 1, wherein the at least two lens groupscomprise at least one positive-powered lens or at least onenegative-powered lens having an Abbe number ranging between 31 and 48,and the flat diffraction lens has an Abbe number ranging between 31 and48.
 4. The collimating lens of claim 1, wherein the at least two lensgroups comprise a plurality of flat lens having an Abbe number rangingbetween 45 and
 65. 5. The collimating lens of claim 1 possesses noconvex outer surface.
 6. A collimating lens, comprising: a first lensgroup, a second lens group and a third lens group disposed in an orderfrom an object side to an image side, each of the first lens group andthe third lens group having an aspherical surface; and a flatdiffraction lens arranged in the third lens group and disposed nearestto an image plane; wherein the aspherical surface of the first lensgroup has a positive radius, and the aspherical surface of the thirdlens group has a negative radius.
 7. A collimating lens, comprising: afirst lens group, a second lens group and a third lens group disposed inan order from an object side to an image side, each of the first lensgroup and the third lens group having an aspherical surface; and a flatdiffraction lens arranged in the third lens group and disposed nearestto an image plane; wherein the first lens group includes anegative-powered first lens, a flat second lens and a positive-poweredthird lens in the order from the object side to the image side; thesecond lens group includes a negative-powered fourth lens, a flat fifthlens and a positive-powered sixth lens in the order from the object sideto the image side; and the third lens group includes a positive-poweredseventh lens, a flat eighth lens and the flat diffraction lens in theorder from the object side to the image side.
 8. The collimating lens ofclaim 7, wherein the negative-powered first lens has an asphericalconcave object-side surface and a planar image-side surface; the flatsecond lens has a planar object-side surface and a planar image-sidesurface; the positive-powered third lens has a planar object-sidesurface and an aspherical convex image-side surface; thenegative-powered fourth lens has an aspherical concave object-sidesurface and a planar image-side surface; the flat fifth lens has aplanar object-side surface and a planar image-side surface; thepositive-powered sixth lens has a planar object-side surface and anaspherical convex image-side surface; the positive-powered seventh lenshas an aspherical convex object-side surface and a planar image-sidesurface; the flat eighth lens has a planar object-side surface and aplanar image-side surface; and the flat diffraction lens has a planarobject-side surface and a planar image-side surface.
 9. The collimatinglens of claim 8, wherein the aspherical concave object-side surface ofthe negative-powered first lens has a negative radius, the asphericalconcave object-side surface of the negative-powered fourth lens has anegative radius, and the aspherical convex object-side surface of thepositive-powered seventh lens has a positive radius.
 10. The collimatinglens of claim 7, wherein the negative-powered first lens, thepositive-powered third lens, the negative-powered fourth lens, thepositive-powered sixth lens, the positive-powered seventh lens and theflat diffraction lens have a refractive index ranging between 1.5 and1.6, and have an Abbe number ranging between 31 and
 48. 11. Thecollimating lens of claim 7, wherein the flat second lens, the flatfifth lens and the flat eighth lens have a refractive index rangingbetween 1.5 and 1.6, and have an Abbe number ranging between 45 and 65.